Thought Technology Ltd.
Tech Note 020
How to Record an Accurate EKG and Heart Rate
This illustrated tech-note will help you solve common signal problems quickly
to get the most from your EKG biofeedback system.
In this document we will discuss the two main placement areas, the chest and the
limbs, and how to get the best signal from them.
Troubleshooting mechanical problems
What if the software cannot detect any signal? First, check that the sensor is
properly connected to the encoder. Also, make sure the electrodes are adhering
properly. Verify that the encoder is loaded with batteries, switched on and the
LED is lit. Finally, check the fiber optic connection to the PC.
Electrode placement
To obtain a high-quality EKG, you must prepare the electrode site properly. We
recommend the use of Thought Technology Unigel electrodes. If the electrodes
won't adhere to the skin because of excess hair, perspiration, or oily skin, wipe the
skin with an alcohol or skin prep wipe, and apply a dab of supplementary
conductive gel to the electrode. If you have tried several placements in the
process of obtaining the optimum signal, it is a good idea to apply a fresh
electrode to the prepared site. If your placement requires gel, use EKG type
conductive gel, not other nonconductive pastes. Place electrodes on fleshy areas
and avoid bony prominence, large muscle and hairy areas. If the client is thin, you
might have to vary the sites slightly to keep electrodes off the ribs. Having applied
the electrodes, make sure the wires aren't pulling on them.
Chest Placements
Chest placements are normally the most reliable and
give the cleanest signals. However they have obvious
disadvantages over the less invasive limb placements.
The standard placement for Thought Technology’s
EKG leads is as shown in the diagram. If you put the
positive and negative the wrong way around when
using CardioPro it may inform you of the incorrect
polarity.
MAR 462-01
Thought Technology Ltd.
Tech Note 020
The standard placements assume an average
positioning of the heart. There may be
anatomical variations between people, which
affect the heart’s positioning in the chest. If after
trying the standard position the signal is not clear
try adjusting the positive or negative electrodes.
Start by moving the positive electrode to the left,
if this does not improve the signal replace it to the
original position and try moving the negative one.
If it is necessary to move the electrodes, you may
have to replace them with fresh ones once you
have identified the optimum position.
Limb Placements
The limbs act as electrical extensions of the body. There are two types of limb
placement: Wrist, wrist and leg or just wrist to wrist. The wrist to wrist is the
easiest to set up and most flexible for the client. To reduce the noise on these
placements move the electrodes higher on the limbs, limb placement is more
susceptible to movement artifact, if you cannot get a stable signal return to the
chest placement. For stable wrist to wrist placements have the client relax their
arms and shoulders and rest the lower arms next to their sides not elevated on the
chair arms.
MAR 462-01
Thought Technology Ltd.
Tech Note 020
What should the EKG signal look like?
The above trace is a normal well-recorded EKG signal, there is no drift or noise and a
sufficiently large R and S spike for the computer to reliably read the heart rate and interbeat-interval.
Solving problems with the tracing
Noise - Poor electrode placement, client movement, muscular tension, can cause “Noise”
or artifact. To eliminate artifact, check electrode connections, move the limb electrodes
higher on the limb, and encourage the client to relax. Clip the encoder to the belt of the
client and move the client further from the computer, and secure any excess sensor wiring
beneath clothing where possible. The trace below clearly has noise, the human eye can
easily pick out the beats but for the computer the noise can disguise the beats.
Signal Drift - Client movement, poor skin preparation and electrode contact, dry
electrodes, respiratory interference, and electrode movement can cause a wandering
baseline. To eliminate a wandering baseline, apply fresh gelled electrodes, encourage the
client to relax and hold still momentarily, and check electrode positions. Ask him to hold
his breath and not to talk for 3 to 6 seconds if he can.
Electrical Noise - Improper grounding of electrical equipment, faulty electrodes, and
poor electrode contact can cause electrical or 50 or 60-cycle interference (indicated by
the thickened baseline). This is minimized in Thought Technology equipment by the
encoder’s appropriate filtering. Maximize the distance between the encoder and sources
of electrical noise such as the computer.
Getting it right the first time - By making these guidelines part of your routine, you can
eliminate many avoidable problems--and correct the unavoidable ones quickly.
MAR 462-01